Ambient Light Sensor Window Coatings for Electronic Devices

ABSTRACT

An electronic device may have a display with a cover layer. An ambient light sensor may be aligned with an ambient light sensor window formed from an opening in a masking layer on the cover layer in an inactive portion of the display. To help mask the ambient light sensor window from view, the ambient light sensor window may be provided with a black coating that matches the appearance of surrounding masking layer material while allowing light to reach the ambient light sensor. The black coating may be formed from a black physical vapor deposition thin-film inorganic layer with a high index of refraction. An antireflection layer formed from a stack of dielectric layers may be interposed between the black thin-film inorganic layer and the display cover layer.

This application is a continuation of U.S. patent application Ser. No.15/293,204, filed Oct. 13, 2016, which claims the benefit of provisionalpatent application No. 62/270,295, filed Dec. 21, 2015, each of which ishereby incorporated by reference herein in its entirety.

FIELD

This relates generally to electronic devices and, more particularly, toelectronic device window coatings.

BACKGROUND

Electronic devices often contain displays. A display may have an activearea with pixels that display images for a user and an inactive areaalongside the active area. A layer of glass may serve as a protectivedisplay cover layer. The layer of glass may overlap the active area andthe inactive area. To hide internal components from view, the innersurface of the inactive area may be covered with an opaque masking layersuch as a layer of black ink. Windows in the display cover layer may beformed from openings in the opaque masking layer. Light-sensitivecomponents may be aligned with the windows. For example, an ambientlight sensor may be aligned with a window in a display.

To improve the outward appearance of the display cover layer in theinactive area, ambient light sensor windows may be covered with coatingsof dark ink. Dark ink coatings for ambient light sensor windows aresometimes referred to as ambient light sensor inks. The presence of theambient light sensor ink on an ambient light sensor will darken theoutward appearance of the ambient light sensor window and thereby helpvisually blend the ambient light sensor window with surrounding portionsof the layer of black ink in the inactive area. At the same time, theambient light sensor ink will be sufficiently transparent to allowambient light to reach the ambient light sensor that is aligned with theambient light sensor window.

Although the presence of ambient light sensor ink on an ambient lightsensor window may help improve device aesthetics, the presence of theambient light sensor ink may introduce non-ideal characteristics to anambient light sensor system. For example, ambient light sensor readingsmay vary as a function of the angle of incidence of incoming ambientlight with respect to the ambient light sensor system.

SUMMARY

An electronic device may have a display with a cover layer. The coverlayer may overlap an active area of the display that has an array ofpixels that display images. The cover layer may also overlap an inactivearea of the display without pixels. The inactive area of the display mayhave an opaque masking layer such as a layer of black ink.

An ambient light sensor may be aligned with an opening in the opaquemasking layer that serves as an ambient light sensor window. To helpmask the ambient light sensor window from view, the ambient light sensorwindow may be provided with a black coating or other dark coating thatmatches the appearance of the black ink while allowing light to reachthe ambient light sensor.

The black coating may include a black physical vapor depositionthin-film inorganic layer with a high index of refraction. The thin-filminorganic layer may be, for example, a metal nitride such as aluminumtitanium nitride. An antireflection and color adjustment layer may beinterposed between the black thin-film inorganic layer and the displaycover layer. The antireflection and color adjustment layer may be formedfrom a stack of dielectric layers such as a stack of metal oxide layerswith alternating higher and lower indices of refraction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an illustrative electronic device inaccordance with an embodiment.

FIG. 2 is a cross-sectional side view of a portion of an illustrativeelectronic device with a window and an aligned light-based componentsuch as an ambient light sensor in accordance with an embodiment.

FIG. 3 is a cross-sectional side view of a portion of a display with acoated window in accordance with an embodiment.

FIG. 4 is a cross-sectional side view of an illustrative window with acoating in accordance with an embodiment.

FIG. 5 is a diagram showing an illustrative stack of inorganicdielectric layers that may be used to implement an antireflection andcolor adjustment layer for a window coating in accordance withembodiment.

FIG. 6 is a cross-sectional side view of an illustrative coating layershowing how the index of refraction of the layer affects optical pathlengths in the layer in accordance with an embodiment.

FIG. 7 contains a pair of graphs in which the transmission of anillustrative coating layer has been plotted as a function of wavelengthfor two different index of refraction values in accordance with anembodiment.

DETAILED DESCRIPTION

Electronic devices may be provided with displays. A display may have anactive area containing an array of pixels that is used to display imagesand an inactive area that is free of pixels. Circuitry and internaldevice components may be mounted under the inactive area.

A protective display cover layer for the display may be formed from alayer of transparent material. The display cover layer may overlap boththe active area and the inactive area of the display. The portion of thedisplay cover layer that overlaps the active area is free of ink and istransparent. An inner surface of the portion of the display cover layerthat overlaps the inactive area may be coated with an opaque maskinglayer to help hide internal structures in the device from view by auser. The opaque masking layer may be formed from a polymer with lightabsorbing particles or other suitable opaque structure. The opaquemasking layer may be, for example, a layer of black ink or an opaquelayer of another color.

Openings may be formed in the opaque masking layer to formlight-transmitting windows. These windows, which may sometimes bereferred to as optical windows or light windows, may be used toaccommodate light-based components. For example, a camera may captureimages through a window in a display cover layer, an ambient lightsensor may make measurements of ambient light levels through a window inthe display cover layer, and a light-based proximity sensor may be usedto make proximity sensor measurements though a window in the displaycover layer. In some situations (e.g., when forming windows forcomponents such as cameras that operate at visible light wavelengths),the windows may be transparent at visible wavelengths and may be free ofany coating layers. In other situations, such as when forming a windowfor an ambient light sensor, it may be desirable coat the window so asto at least partly obscure the window. This may be accomplished, forexample, by coating an ambient light sensor window with a dark coatingthat transmits sufficient ambient light to an ambient light sensor toallow the ambient light sensor to make ambient light measurements. Thedark appearance of the coating may allow the ambient light sensor windowto blend in with the appearance of nearby portions of the black ink orother opaque masking layer in the inactive area.

In general, window coatings for ambient light sensors may have anysuitable color (e.g., white, gray, black, or other colors). Thesecoatings may transmit any suitable amount of light (e.g., thetransmission of these coatings may be greater than 50%, less than 50%,5-20%, less than 30%, less than 20%, less than 10% or other suitablevalue). Coatings may be provided on windows for infrared and visiblelight cameras, for infrared components, for light sensing arraysassociated with user input-output devices (e.g., touch sensors orfingerprint sensors), for proximity sensors, or for any other suitablelight-based component in device 10. Configurations in which an ambientlight sensor window is provided with a coating may sometimes bedescribed herein as an example. This is, however, merely illustrative.Coatings may be provided on any suitable transparent window structure indevice 10.

To ensure that a window coating has a desired appearance (e.g., adesired reflectivity, a desired color, a desired transmission at certainwavelengths, etc.), window coatings may be formed using thin-filmstacks. For example, multiple thin layers of inorganic material may bedeposited onto the inner surface of a display cover layer using physicalvapor deposition techniques or other suitable techniques. By tuning thenumber of layers, the thicknesses of the layers, and the materials usedin the layers of a coating, the coating can be provided with a desiredexternal appearance and transmission properties. For example, a coatingon the inner surface of an ambient light sensor window may serve as anantireflection and color adjustment layer that adjusts the amount ofreflection from the window and the color of the window (e.g., to abluish black color in configurations in which the opaque maskingmaterial in the inactive area of the display has a bluish blackappearance). The coating may also be provided with thin-film layer ofinorganic material that absorbs light (e.g., to ensure that the coatingappears sufficiently black to blend with surrounding opaque maskingstructures).

FIG. 1 is a perspective view of an illustrative electronic device of thetype that may include a display with windows for light-based componentssuch as an ambient light sensor. Electronic device 10 may be a computingdevice such as a laptop computer, a computer monitor containing anembedded computer, a tablet computer, a cellular telephone, a mediaplayer, or other handheld or portable electronic device, a smallerdevice such as a wrist-watch device, a pendant device, a headphone orearpiece device, a device embedded in eyeglasses or other equipment wornon a user's head, or other wearable or miniature device, a television, acomputer display that does not contain an embedded computer, a gamingdevice, a navigation device, an embedded system such as a system inwhich electronic equipment with a display is mounted in a kiosk orautomobile, equipment that implements the functionality of two or moreof these devices, an accessory (e.g., earbuds, a remote control, awireless trackpad, etc.), or other electronic equipment. In theillustrative configuration of FIG. 1, device 10 is a portable devicesuch as a cellular telephone, media player, tablet computer, or otherportable computing device. Other configurations may be used for device10 if desired. The example of FIG. 1 is merely illustrative.

In the example of FIG. 1, device 10 includes display 14. Display 14 hasbeen mounted in housing 12. Housing 12, which may sometimes be referredto as an enclosure or case, may be formed of plastic, glass, ceramics,fiber composites, metal (e.g., stainless steel, aluminum, etc.), othersuitable materials, or a combination of any two or more of thesematerials. Housing 12 may be formed using a unibody configuration inwhich some or all of housing 12 is machined or molded as a singlestructure or may be formed using multiple structures (e.g., an internalframe structure, one or more structures that form exterior housingsurfaces, etc.). Openings may be formed in housing 12 to formcommunications ports, holes for buttons, and other structures.

Display 14 may be a touch screen display that incorporates a layer ofconductive capacitive touch sensor electrodes or other touch sensorcomponents (e.g., resistive touch sensor components, acoustic touchsensor components, force-based touch sensor components, light-basedtouch sensor components, etc.) or may be a display that is nottouch-sensitive. Capacitive touch sensor electrodes may be formed froman array of indium tin oxide pads or other transparent conductivestructures.

Display 14 may have an active area AA that includes an array of pixels.The array of pixels may be formed from liquid crystal display (LCD)components, an array of electrophoretic pixels, an array of plasmadisplay pixels, an array of organic light-emitting diode pixels or otherlight-emitting diode pixels, an array of electrowetting pixels, orpixels based on other display technologies.

Display 14 may be protected using a display cover layer such as a layerof transparent glass, clear plastic, transparent ceramic, sapphire orother transparent crystalline material, or other transparent layer(s).The display cover layer may have a planar shape, a convex curvedprofile, a concave curved profile, a shape with planar and curvedportions, a layout that includes a planar main area surrounded on one ormore edges with a portion that is bent out of the plane of the planarmain area, or other suitable shape. Openings may be formed in thedisplay cover layer to accommodate button 16, ports such as speaker port18, and other structures.

Display 14 may have an inactive border region such as inactive area IAthat runs along one or more of the edges of active area AA. Inactivearea IA may be free of pixels for displaying images and may overlapcircuitry and other internal device structures in housing 12. To blockthese structures from view by a user of device 10, the underside of thedisplay cover layer for display 14 may be coated with an opaque maskinglayer in inactive area IA. The opaque masking layer may have anysuitable color. With one suitable arrangement, which may sometimes bedescribed herein as an example, the opaque masking layer in regions IAof display 14 may be formed from a layer of black ink that is opaque atvisible wavelengths.

Openings may be formed in the black ink coating on the underside of thedisplay cover layer in inactive area IA. These openings may form windowsfor light-based components in device 10. In the example of FIG. 1,window 20 has been formed in inactive area IA along an upper edge ofdisplay 14. In general, windows such as window 20 may be formed in anysuitable portion of display 14 (i.e., in other portions of inactive areaIA) or other transparent structures in device 10. The configuration ofFIG. 1 is merely illustrative.

Window 20 may be circular, rectangular, or may have other suitableshapes. Window 20 may be aligned with a light-based component such as anambient light sensor and may have an ambient light sensor coating. Theambient light sensor coating is sufficiently transparent to allowambient light to reach the ambient light sensor while being sufficientlyclose in appearance to surrounding portions of the opaque black maskinglayer in inactive area IA to help obscure window 20 from view by a userof device 10.

FIG. 2 is a cross-sectional side view of a portion of device 10 of FIG.1 in the vicinity of window 20 taken along line 22 of FIG. 1 and viewedin direction 24. As shown in FIG. 2, display 14 may have a transparentlayer such as display cover layer 30. Display cover layer 30 may beformed from a transparent material such as glass, plastic, sapphire orother crystalline material, transparent ceramic, etc. In active area AA,display 14 may contain structures 32 (e.g., an organic light-emittingdiode display layer, a liquid crystal display module, etc.) with anarray of pixels 34 for displaying images.

The inner surface of display cover layer 30 may be coated with one ormore layers of material in inactive area IA. In the example of FIG. 2,the underside of display cover layer 30 in inactive area IA has beencoated with opaque masking layer 36. Opaque masking layer 36 may be, forexample, a layer of black ink. Opening 40 for window 20 may be formed inopaque masking layer 36. Ambient light sensor coating layer 38 mayoverlap opening 40 and may provide window 20 with a desired appearance.For example, coating layer 38 may include antireflection structures forsuppressing reflections from window 20, thin-film spectral tuningstructures for adjusting the color of window 20, and structures forabsorbing sufficient light to darken the appearance of window 20 andthereby match the appearance of masking layer 36.

As shown in FIG. 2, a light-based component such as component 42 may bealigned with window 20. Component 42 may be an ambient light sensor suchas a color sensing ambient light sensor that measures ambient light 44.A color sensing ambient light sensor may have an array of detectors eachof which measures the amount of light in a different respective colorchannel (e.g., blue, red, green, channels of other colors, channels thatrespond to combinations of two different colors, etc.). This allows thecolor sensing ambient light sensor to determine the color (colorcoordinates, color temperature, etc.) of ambient light in theenvironment surrounding device 10. The color sensing ambient lightsensor may, for example, detect cold ambient lighting conditions when auser is in an outdoors shaded environment and warm ambient lightingconditions when a user is in an indoors tungsten lighting environment(as examples). Color information from the color ambient light sensor maybe used to make color corrections to the colors displayed by pixels 34in display 14 or to make other adjustments to the performance of device10. If desired, one or more of the color channels in sensor 42 may beresponsive to infrared light. Monochromatic ambient light sensors mayalso be used in device 10 (i.e., sensor 42 may be a monochromaticambient light sensor).

In the example of FIG. 2, window coating 38 has been deposited over theinner surface of opaque masking layer 36 after opening 40 has beenformed in layer 36. Layer 36 may be deposited and patterned using screenprinting or other suitable techniques. If desired, coating 38 may bedeposited on the inner surface of display cover layer 30 beforedepositing layer 36 and patterning layer 36 to form opening 40 forwindow 20 (see, e.g., FIG. 3). In configurations in which coating 38 hasa sufficiently opaque appearance, some or all of opaque masking layer 36may be omitted from inactive area IA.

As shown in FIG. 4, incoming ambient light such as ambient light 44 ofFIG. 2 may be characterized by a range of angles of incidence AOI withrespect to surface normal n of the window 20 (i.e., the surface normalof the portion of display cover layer 36 in window 20). Coating 38preferably exhibits a transmission characteristic that is not highlydependent on angle of incidence AOI. The appearance of coating 38 alsopreferably matches that of opaque masking layer 36 in attributes such ascolor and reflectivity.

With one illustrative configuration, coating 38 includes anantireflection and color adjustment layer such as layer 50. Materialssuch as black ink for opaque masking layer 36 may be formed from polymercontaining particles of carbon black or other ink materials that haverelatively low reflectivity. Accordingly, one or more thin-filmdielectric layers or other thin-film layers in layer 50 may be formed ina stack to serve as an antireflection coating. The index of refractionof the one or more layers of antireflection material may be selected toreduce the light reflection from window 20 to a level that matches thelight reflection from opaque masking layer 36.

If desired, the indexes of refraction, materials, and layer thicknessesof the materials in coating 38 (e.g., the spectral tuning structures oflayer 50) may be selected to ensure that coating 38 has a desired color(e.g. a bluish black, or a color with another desirable spectralprofile). Because thin-film interference effects can be used to adjustreflectivity and color, a wide variety of desired reflectivity valuesand colors can be implemented (e.g., by adjusting layer thicknesses,number of layers, and layer materials). Layer 50 can adjustantireflection and color properties associated with coating 38, so layer50 may sometimes be referred to as an antireflection and coloradjustment layer (antireflection layer, spectral tuning layer, coloradjustment coating, etc.).

Coating layer 38 may also include one or more light absorbing layerssuch as layer 52. Layer 52 may, for example, be a dark material thatabsorbs sufficient light to make coating 38 appear black. The thicknessof layer 52 may be sufficiently small to allow some of ambient light 44to pass to ambient light sensor 42.

An illustrative configuration for antireflection and color adjustmentcoating 50 of FIG. 4 is shown in FIG. 5. In the example of FIG. 5,coating 50 has been formed from a stack of six inorganic dielectriclayers (metal oxide layers): three aluminum oxide layers and threetitanium oxide layers. The different index of refraction values foraluminum oxide (index 1.7) and titanium oxide (index 2.7) relative toeach other and relative to the glass (index 1.55) of layer 30 allowlayer 50 to serve as an antireflection layer (reducing reflections ofvisible light from window 20) and as a color adjustment (spectraladjustment) layer for window 20. In general, layer 50 may have anysuitable number of dielectric layers (e.g., alternating higher and lowerindex of refraction layers or other patterns of dielectric layers withdifferent indices of refraction), may have dielectric layers formed frommetal oxides, silicon oxide, silicon nitride, other oxides, nitrides,oxynitride, or other inorganic materials. This stack of thin-film layersmay be deposited using physical vapor deposition techniques (e.g.,sputtering or evaporation) or other suitable deposition techniques.

Light absorption layer 52 may also be an inorganic layer that isdeposited using physical vapor deposition or other suitable depositiontechniques (e.g., layer 52 may be a black physical vapor depositioninorganic layer). To help reduce angle-of-incidence sensitivity, layer52 may be formed from a material that has a relatively high index ofrefraction.

As shown in the cross-sectional side view of layer 62 of FIG. 6,incoming ambient light 44 may be characterized by various differentangles of incidence. The example of FIG. 6 shows how light 44 may havean angle of incidence AOI of 60° or 30° (as examples). In situations inwhich the index of refraction of layer 52 is low (e.g., 1.6 or 1.7 aswith polymer inks), light 44 will travel along paths such as short pathPS-1 and long path PL-1, associated with angles of incidence AOI of 30°and an angle of incidence of 60°, respectively. This can create asignificant path length difference (PL-1 minus PS-1) as the angle ofincidence of ambient light 44 varies. In situations in which the indexof refraction of layer 52 is high (e.g., 2.3 as with a material such asAlTiN or other suitable high-index thin-film inorganic layer), light 44will travel along paths such as short path PS-2 and long path PL-2 (forrespective angles of incidence AOI of 30° and) 60°. Due to the largerrefractive index in this situation, light 44 is refracted more uponentering layer 52 and the path length difference PL-2 minus PS-2 will besmaller than path length difference PL-1 minus PS-1. The reduced pathlength changes that result from different angles of incidence when therefractive index of layer 52 is high help ensure that coating 38 andambient light sensor 42 will be relatively insensitive to variations inambient light angle of incidence.

The simulations of FIG. 7 show the impact of this change in refractiveindex on the light transmission spectrum for an illustrative lightabsorption layer 52 under various illustrative angles of incidence AOIfor light 44. In the graphs of FIG. 7, transmission T (%) has beenplotted as a function of wavelength (in nm) as a function of fivedifferent values for angle of incidence AOI. In the simulation on theright side of FIG. 7, the index of refraction of layer 52 is 1.6 and theresulting spread between the transmission values T is large. In thesimulation on the left side of FIG. 7, the index of refraction of layer52 is 2.3 and the resulting spread between transmission values T atdifferent angles of incidence is reduced. The use of a refractive indexof 2.3 or larger for layer 52 (or at least an index larger than 1.7,larger than 1.8, larger than 1.9, larger than 2.0, larger than 2.1, orlarger than 2.2) will therefore help reduce angle-of-incidencesensitivity for sensor 42. Spectral variations in the transmission ofcoating 38 that do not vary with angle of incidence can be compensatedduring light sensor calibration operations during manufacturing (e.g.,in scenarios in which ambient light sensor 42 is a color ambient lightsensor).

An example of a material that absorbs visible light to produce a blackcolor for coating 38 and window 20 and which may therefore be suitablefor use in forming light absorbing layer 52 in coating 38 is aluminumtitanium nitride. This material has an index of refraction of 2.3 andcan be deposited by sputtering aluminum and titanium in a nitrogenatmosphere (as an example). Other materials may be used, if desired(e.g., metals, dielectrics, nitrides, metal nitrides other than AlTiN,other inorganic materials, etc.). The use of aluminum titanium nitridein forming a visible light absorbing physical vapor deposition thin-filmcoating for window 20 is merely illustrative. The thickness of coatinglayer 52 may be 400 nm, 200-600 nm, less than 700 nm, less than 500 nm,more than 50 nm, more than 100 nm, more than 300 nm, or other suitablethickness and may be deposited using physical vapor deposition or othersuitable deposition techniques. The visible light transmission of layer52 and coating 38 may be less than 50%, less than 30%, less than 20%,less than 10% or other suitable amount. Layer 52 may be a blackinorganic thin-film layer so that coating 38 has a black appearance orlayer 52 and/or coating 38 may be formed from other materials with othercolors. The use of sputtered inorganic layers of material for layer 52allows these layers to be deposited accurately (e.g., film thickness maybe controlled within 2%) and may be smooth, thereby reducing lightscattering that might otherwise make window 20 visible against maskingmaterial 36.

The foregoing is merely illustrative and various modifications can bemade by those skilled in the art without departing from the scope andspirit of the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. An electronic device having an interior and anexterior, the electronic device comprising: a display; a transparentstructure that has a first surface that faces the interior and anopposing second surface; and a coating on the first surface of thetransparent structure, wherein the coating has a physical vapordeposition thin-film coating and a stack of dielectric layers interposedbetween the physical vapor deposition thin-film coating and thetransparent structure.
 2. The electronic device defined in claim 1wherein the transparent structure comprises a display cover layer forthe display.
 3. The electronic device defined in claim 2 wherein thedisplay has an active area and an inactive area and wherein the coatingoverlaps the inactive area.
 4. The electronic device defined in claim 1wherein the physical vapor deposition thin-film coating comprises ametal nitride.
 5. The electronic device defined in claim 4 wherein thephysical vapor deposition thin-film coating comprises aluminum titaniumnitride.
 6. The electronic device defined in claim 1 wherein thetransparent structure comprises a material selected from the groupconsisting of: glass, plastic, ceramic, and sapphire.
 7. The electronicdevice defined in claim 1 further comprising a light sensor, wherein thetransparent structure has a portion forming a window that is alignedwith the light sensor.
 8. The electronic device defined in claim 7wherein the coating is in the window of the transparent structure andwherein light incident on the transparent structure passes through thewindow and the coating to reach the light sensor.
 9. The electronicdevice defined in claim 8 wherein the light sensor is a color sensinglight sensor.
 10. An electronic device having an interior and anexterior, the electronic device comprising: a transparent layer having afirst surface that faces the interior and an opposing second surface; adisplay that is overlapped by the transparent layer; and a coating onthe first surface of the transparent layer, wherein the coating includesa physical vapor deposition thin-film coating and an antireflectioncoating between the physical vapor deposition thin-film coating and thetransparent layer.
 11. The electronic device defined in claim 10 furthercomprising a color sensing light sensor, wherein the transparent layerhas a window and the color sensing light sensor is aligned with thewindow.
 12. The electronic device defined in claim 11 wherein thecoating is interposed between the color sensing light sensor and thewindow.
 13. The electronic device defined in claim 10 wherein theantireflection coating comprises a plurality of thin-film layers, andwherein at least some of the thin-film layers of the plurality ofthin-film layers have different indices of refraction.
 14. Theelectronic device defined in claim 13 wherein the plurality of thin-filmlayers are formed from materials selected from the group consisting of:metal oxides, silicon oxide, silicon nitride, and oxynitride.
 15. Anelectronic device comprising: a transparent structure; a display that isoverlapped by the transparent structure; a coating on a portion of thetransparent structure, wherein the coating comprises a physical vapordeposition thin-film coating and a stack of dielectric layers interposedbetween the physical vapor deposition thin-film coating and thetransparent structure.
 16. The electronic device defined in claim 15wherein the physical vapor deposition thin-film coating is configured toallow some light incident on the transparent structure to pass throughthe coating.
 17. The electronic device defined in claim 16 wherein thephysical vapor deposition thin-film coating is less than 500 nm thick.18. The electronic device defined in claim 15 wherein the stack ofdielectric layers comprises a stack of metal oxide layers havingalternating higher and lower indices of refraction.
 19. The electronicdevice defined in claim 15 wherein the transparent structure comprises awindow, the electronic device further comprising: a light sensor in thehousing that is overlapped by the window in the transparent structure.20. The electronic device defined in claim 19 wherein the light sensoris a color sensing light sensor and wherein the coating is interposedbetween the color sensing light sensor and the transparent structure.